Light water nuclear reactors (LWR) typically produce steam at about 1000 psi having little or no superheat. When this steam is expanded in a steam turbine a significant fraction of the flow condenses with a consequent loss of power. Further, so-called "nuclear" turbine designs must be employed having means therein to strip this moisture out of the steam flow path in order to recover efficient turbine performance. This need to remove moisture complicates the turbine design and results in more costly equipment. When reheaters and cross-over moisture separators are employed to reduce the moisture content of the steam flow, penalties in the form of pressure losses are introduced in the system.
Attempts have been made to improve the efficiency of LWR power generating plants by the utilization of fossil-firing to superheat the steam output and then introducing this superheated steam to a conventional steam turbine-generator set. The major shortcoming of this simple solution, however, is the combination in such a superheater of extremely high combustion temperatures and low heat transfer coefficients. This combination presents the ever-present risk of increased reactor down-times resulting from overheating of the superheater tubes and consequent failures of fossil-fired superheaters.
There is a very definite need for means for superheating steam from LWR's without danger of overheating the superheater tubes. The instant invention offers one solution to the problem.
"Superheating" or "reheating" are defined as increasing the temperature of steam substantially above its saturation temperature. Steam produced in a light water reactor has a temperature of about 550.degree. F. It is preferable to be able to raise this temperature to about 1000.degree.-1100.degree. F., thereby significantly improving the efficiency of power generation by LWR's. In the case of reheating, the steam product stream from a LWR may have passed through rotating equipment before the reheating step is accomplished to increase the temperature of the steam substantially above its saturation temperature.